Some wireless telecommunications systems employ a time division multiplexing scheme. The transmission time available for each of one or more frequencies is divided into slots. By way of example, in GSM each frequency is divided into eight slots collectively referred to as a frame, and these slots repeat in time.
In this description, assignment refers to signalling used to identify slots that are made available to a given UE. In this description, allocation refers to the actual reception/transmission of data on specific slots. An allocation will necessarily be a subset or all of the available assignment. Multiple UEs can have the same or overlapping assignments, and allocation will be used to avoid collisions. A particular allocation of slots within a frame or series of frames is typically repeated over a period of time. This is referred to as a TBF (temporary block flow). The TBF is a unidirectional entity: an uplink TBF relates to uplink assignment/allocation and a downlink TBF relates to downlink assignment/allocation. The slot numbering for the uplink is offset from the slot numbering for the downlink such that a downlink slot and an uplink slot with the same number can be assigned and allocated on both the downlink and the uplink without requiring the UE to receive and transmit at the same time. For a given user equipment (UE), the same physical time slot can be assigned and/or allocated for either the uplink or the downlink, but not both. However, due to the offset numbering scheme described above, slots having the same slot number can be assigned and allocated on both the uplink and downlink.
Multiple UEs in a given area share these time slots. Whenever each UE has data, it will, based on an uplink allocation mechanism, send data in the uplink direction. The network will also send data in the downlink direction on these slots to multiple mobiles. For example, in a first frame slot 0 may contain data for a first UE, while in a next frame, the same slot may contain data for a second UE. Since a slot is a very small time unit, a slot may be allocated to a UE over multiple consecutive frames. For example, a BTTI (Basic Transmit Time Interval) block consists of a slot allocated over four consecutive frames. For example, frame 1 slot 1, frame 2 slot 1, frame 3 slot 1 and frame 4 slot 1 make up a BTTI block. In some implementations, a frame is approximately 5 ms in duration, such that a BTTI block will span over four frames, or a 20 ms interval. A BTTI TBF is a TBF which uses BTTI blocks.
An RTTI (Reduced Transmit Time Interval) block uses the same frame structure introduced above, but an RTTI block consists of a pair of slots during a first frame, and a pair of slots during the next frame such that an RTTI block will span over two frames or a 10 ms interval. An RTTI TBF is a TBF which uses RTTI blocks. The transmission interval for an RTTI block compared to a BTTI block is reduced by half. Because of the pairing restriction, RTTI TBFs can only be used in assignments where there is an even number of uplink slots or an even number of downlink slots. For example, RTTI TBFs can be used in 2+2, 4+2, and 2+4 multi-slot-pairs of assignment (based on the UE multi-slot capability), where the “n+m” nomenclature indicates a pair of assignments including first assignment of n receive slots and a second assignment of m transmit slots.
RTTI blocks are always assigned in pairs of slots. Thus, a 2+2 assignment represents a first assignment of a pair of slots for reception, and a second assignment of a pair of slots for transmission. A 4+2 assignment represents a first assignment of two pairs of slots for reception, and a second assignment of one pair of slots for transmission.
Specifically, there may be multiple classes of user equipment that each accommodate a specific maximum number of downlink or receive slots, a specific maximum number of uplink or transmit slots, a minimum time gap between receiving and transmitting, and a minimum time gap between transmitting and receiving. A particular set of 45 classes is defined in 3GPP TS 45.002 V7.6.0 Annex B.
In applications that would benefit from using RTTI TBFs, the multi-slot capability of certain UE multi-slot classes cannot be exploited fully due to the pairing requirement. In a specific example, a class 12 UE supports a maximum of four receive timeslots, a maximum of four transmit timeslots, such that the sum of the total timeslots allocated cannot exceed five. However, of the available RTTI multi-slot assignments, only the 2+2 pair of assignments will accommodate the constraints of the class 12 UE. This means that the user equipment has an additional receive or transmit slot capability that it is not able to utilize when in RTTI mode. In more general terms, for the specific class definitions referred to above, this situation exists where the desired number of transmit slots and/or the desired number of receive slots is an odd number that is greater than or equal to three.
This limitation can be addressed by assigning multiple TBFs to the UE for the uplink and/or the downlink. For example, the 3+2 or 2+3 capability of a class 12 UE could be implemented with 2+2 RTTI TBF pair of assignments in combination with a BTTI TBF assignment in the downlink or uplink respectively. Multiple TBFs may be appropriate when the UE is supporting multiple PDP (packet data protocol) contexts that have different QoS (quality of service) or other service parameters. However setting up and managing multiple TBFs causes an increase in signalling load, and requires support of this feature on both the network and the UE. This solution is inappropriate when a single application (for example FTP, HTTP) needs to benefit from RTTI and also at the same time needs to exploit the full multi-slot capability of the UE in the limiting cases described above.